NASA Makes Leap In Snowpack Measurements

In the Northwest snowpack is about more than a downhill run. Every winter hydologists make the regular trek up Oregon mountains through the season measuring the depth of the snowpack and that data is used to estimate how much water will be available in the spring and summer for power generation, salmon passage, and farm irrigation all of which are contentious issues in a low water year.

The measurement methods haven't changed very much in decades and requires some experience on the hydrologist's part to generate accurate data. Basically, the depth of the snowpack is measured with a stick and a core sample is taken to determine the moisture content of the snow. The outcome of that frequent testing can mean the difference between growing crops, or protecting salmon runs along with the consideration of how much cheap hydropower will be available to sell to utilities impacting ratepayers.

A new NASA airborne mission has created the first maps of the entire snowpack of two major mountain watersheds in California and Colorado, producing the most accurate measurements to date of how much water they hold.

The data from NASA's Airborne Snow Observatory mission will be used to estimate how much water will flow out of the basins when the snow melts. The data-gathering technology could improve water management for 1.5 billion people worldwide who rely on snowmelt for their water supply.

"The Airborne Snow Observatory is on the cutting edge of snow remote-sensing science," said Jared Entin, a program manager in the Earth Science Division at NASA Headquarters in Washington. "Decision makers like power companies and water managers now are receiving these data, which may have immediate economic benefits."

The mission is a collaboration between NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., and the California Department of Water Resources in Sacramento.

A Twin Otter aircraft carrying NASA's Airborne Snow Observatory began a three-year demonstration mission in April that includes weekly flights over the Tuolumne River Basin in California's Sierra Nevada and monthly flights over Colorado's Uncompahgre River Basin. The flights will run through the end of the snowmelt season, which typically occurs in July. The Tuolumne watershed and its Hetch Hetchy Reservoir are the primary water supply for San Francisco. The Uncompahgre watershed is part of the Upper Colorado River Basin that supplies water to much of the western United States.

The mission's principal investigator, Tom Painter of JPL, said the mission fills a critical need in an increasingly thirsty world, initially focusing on the western United States, where snowmelt provides more than 75 percent of the total freshwater supply.

"Changes in and pressure on snowmelt-dependent water systems are motivating water managers, governments and others to improve understanding of snow and its melt," Painter said. "The western United States and other regions face significant water resource challenges because of population growth and faster melt and runoff of snowpacks caused by climate change. NASA's Airborne Snow Observatory combines the best available technologies to provide precise, timely information for assessing snowpack volume and melt."The observatory's two instruments measure two properties most critical to understanding snowmelt runoff and timing. Those two properties have been mostly unmeasured until now.

A scanning lidar system from the Canadian firm Optech Inc. of Vaughan, Ontario, measures snow depth to determine the first property, snow water equivalent with lasers. Snow water equivalent represents the amount of water in the snow on a mountain. It is used to calculate the amount of water that will run off.

An imaging spectrometer built by another Canadian concern, ITRES of Calgary, Alberta, measures the second property, snow albedo. Snow albedo represents the amount of sunlight reflected and absorbed by snow. Snow albedo controls the speed of snowmelt and timing of its runoff.

By combining these data, scientists can tell how changes in the absorption of sunlight cause snowmelt rates to increase.The Airborne Snow Observatory flies at an altitude of 17,500 feet - 22,000 feet (5,334 to 6,705 meters) to produce frequent maps that scientists can use to monitor changes over time. It can calculate snow depth to within about 4 inches (10 centimeters) and snow water equivalent to within 5 percent. Data are processed on the ground and made available to participating water managers within 24 hours.